1. Field of the Invention
The invention relates to an on-demand ink jet recording head that forms characters and graphics on a recording medium with dots by expelling ink droplets thereto in accordance with input information. More particularly, the invention is directed to a structure having electrodes and piezoelectric vibrating elements formed on a surface of a vibrating plate as well as to a method of manufacturing such structure. The vibrating plate constitutes part of the pressure producing chambers. The electrodes and the piezoelectric vibrating elements are formed integrally with the pressure producing chambers by baking.
2. Related Art
An ink jet recording head has a structure such that an ink droplet is expelled by causing a piezoelectric element to be abutted against a small pressure producing chamber and increasing the pressure of ink within the pressure producing chamber by displacement of a vibrating plate. As a result, precision working and fabricating techniques are required in the manufacture of the ink jet recording head, which elevates the cost.
To overcome this problem, a structure shown in FIG. 19 has been proposed attaching importance to the fact that the piezoelectric vibrating element, the vibrating plate constituting the pressure producing chamber, and the pressure producing chamber forming member can be made of ceramic. That is, a vibrating plate 90 formed by rolling a green sheet, which is a ceramic material, to a predetermined thickness and a pressure producing chamber forming member 94 having a pressure producing chamber 91 formed in advance by punching or machining a green sheet with a laser beam, which is also a ceramic material, are pressed and baked. Then, an electrode 93 is formed on the vibrating plate 90 and a piezoelectric vibrating element 92 is formed on the electrode 93 by baking.
Such an integrally baked ink jet recording head has the advantage of simple fabrication that involves only the steps of coating and baking a paste-like piezoelectric element by means of a printing technique. Further, since the pressure producing chamber forming member is integrated with the vibrating plate by baking, defective bonding such as observed in bonds formed by adhesives can be eliminated, which is an advantage in reliably preventing ink leakage.
However, the piezoelectric vibrating element, being such a small piece, is hard to uniformly coat to the corresponding drive electrode. Particularly, inconsistency in the bond of each piezoelectric vibrating element 92 with a peripheral edge 95 of the electrode 93 leads to inconsistency in the effective operation region between the piezoelectric vibrating elements, which in turn causes inconsistency in the ink expelling characteristic of each nozzle opening.
By the way, in the steps of depositing the electrode 93 on the surface of the vibrating plate 90, which is made of ceramic, and depositing the piezoelectric vibrating element 92 on the surface of the electrode 93 by baking, the vibrating plate 90 generally flexes as shown in FIG. 20. That is, the vibrating plate 90 flexes toward the pressure producing chamber 91 at a central portion of the pressure producing chamber 91 due to a difference in the rate of contraction between the piezoelectric vibrating element 92 and the electrode 93 at the time of baking. As a result, a permanent deformation in which a part 92a (the cross-hatched region in FIG. 20) of the lower region of the piezoelectric vibrating element 92 projects toward the pressure producing chamber 91 tends to occur.
When the piezoelectric vibrating element 92 that has been deformed is caused to contract for expelling ink by applying a drive signal thereto, contracting forces in such horizontal directions indicated by arrows A1, A1 are generated as far as to the part 92a of the lower region, thereby drawing in the horizontal directions the vibrating plate 90 that has already been flexed. As a result, a part of the contracting force draws walls 94a, 94b of the pressure producing chamber forming member 94 in directions indicated by arrows C1, C2 through the vibrating plate 90. Since the walls 94a, 94b of the pressure producing chamber forming member 94 are shared in common with the adjacent pressure producing chambers 91, the contraction of a single pressure producing chamber 91 is transmitted to other pressure producing chambers 91, causing crosstalk or cancelling out a force B1 that contributes to the ink expelling operation when adjacent piezoelectric vibrating elements 92, 92 are driven simultaneously, which impairs ink expelling efficiency.
The displacement of the vibrating plate 90 in the case where a single piezoelectric element is driven is different from that in the case where a plurality of adjacent piezoelectric vibrating elements 92 are driven simultaneously, the difference being approximately twice. This causes differences in the ink droplet expelling speed and the amount of ink expelled, the differences being approximately 1.5 times.